In a November appearance with conservative policy advocate David Horowitz, Caddell called the SEIU "thugs" and said environmentalists were out to "deconstruct capitalism."

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Hours after a video of the comments was posted on the political website, ColoradoPols.com, the Romanoff campaign announced it had removed Caddell from its campaign team.

"Today a video was posted on ColoradoPols, in which Pat expressed views that were completely at odds with Andrew's campaign, his career and his commitment to the environment and to Colorado's working families. Andrew heard those comments for the first time this afternoon and ended Pat's role in the campaign," said Romanoff spokesman Dean Toda in a statement.

While Caddell was an unpaid consultant, his firing comes roughly two weeks after the Romanoff campaign bulked up its staff and touted the upgrade as a significant addition in their fight against "special interests and corporate power."

In his reference to the Service Employees International Union, Caddell targeted President Andy Stern. "He said, 'we believe in the power of persuasion, and if that doesn't work, we believe in the persuasion of power.' Now if you don't know what that phrase means, and how they're using this, then you don't understand how exactly dangerous this all is. Because those guys are thugs, the SEIU," Caddell says.

The veteran strategist also questions the mission of public employee unions. "I don't understand what they're doing. I mean, who are they protecting us from, the taxpayers?" Caddell asks.

Caddell offers an even more harsh assessment of environmentalists. "The whole idea of the environmental movement isn't to clean up the environment, or to do what we need to do or to get jobs," he said. "It is to basically deconstruct capitalism."

Romanoff, the former state House Speaker, recently won the endorsement of the United Food and Commercial Workers and the Council of Teamsters in Colorado.

The flap comes at the same time the appointed Democratic senator he's trying to upend is also attempting to burnish his credentials with the progressive wing of the party.

Sen. Michael Bennet (D-Colo.) joined three other Democratic senators Tuesday in asking Senate Majority Leader Harry Reid (D-Nev.) to use reconciliation, a controversial procedure requiring only 51 votes, to push for a public option in health care legislation.

"Put simply, including a strong public option is one of the best, most fiscally responsible ways to reform our health insurance system," the letter says. "Although we strongly support the important reforms made by the Senate-passed health reform package, including a strong public option would improve both its substance and the public’s perception of it."

Sen. Sherrod Brown (D-Ohio), Sen. Jeff Merkley (D-Ore.) and Sen. Kirsten Gillibrand (D-N.Y.), another appointed senator who faces a potential primary challenge, are the three others who joined Bennet in penning the letter.